1. Field of the Invention
The present invention relates to a capping device for an ink jet head provided with ink suction function. In particular, the present invention is directed to means for preventing undesirable mixture of different color inks after sucking the different color inks from a multi-ink jet head.
2. Description of the Prior Art
In the art there is known an ink jet head provided with a negative pressure generating function to suck the residual ink from the head after use. Also, such capping device is known which is exclusively used for a multi-ink jet head having two or more ink jet heads.
The use of such a capping device for a multi-ink jet head, however, produces the problem of undesirable mixture of different color inks. The individual heads in a multi-ink jet head are so designed as to jet different color inks from the respective nozzles. Since the nozzles are in communication with each other, if the multi-ink jet head is left standing with the capping device fitted thereto after ink suction, there is caused a mixture of the different color inks by the phenomenon of ink dispersion. This problem will be described hereinafter in further detail with reference to FIG. 1. In FIG. 1 showing a conventional multi-ink jet head with a capping device, the multi-ink jet head 1 is composed of four individual head units 1-1 to 1-4 assembled together. Although not shown, the multi-ink jet head is mounted on a carriage for movement together with the carriage. The individual head units 1-1 to 1-4 have the same structure comprising an ink storing subsidiary tank and a nozzle to jet the ink from the subsidiary ink tank. The inks contained in and jetted from the individual heads are different in color from each other. As shown in FIG. 1, the nozzles are completely closed by a cap 2. While closed by the cap 2, the nozzles are sucked by a suction pump 4 through tubes 3 in the manner of negative pressure suction. This suction is necessary to return the nozzles to the condition in which they are ready for printing. The tubes 3 are in communication with each other as seen in FIG. 1. Therefore, if the multi-ink jet head 1 is left standing with the nozzles capped with the cap 2, then the different color inks are mixed together in the respective nozzles and in the respective subsidiary ink tanks.